Optical distance measuring device

ABSTRACT

A measuring device for optically measuring a distance to a target object including an emitter device for emitting an optical measuring beam to the target object, a capturing device comprising a detection surface for detecting an optical beam returned by the target object, and an evaluation device. The detection surface has a plurality of pixels, each pixel having at least one light-sensitive element and each of the plurality of pixels is connected to the evaluation device. The emitting device and the capturing device are configured in such a manner that the optical measurement beam returned by the target object simultaneously illuminates a plurality of pixels. The evaluation device is configured in such a manner that detection signals of a plurality of pixels are guided to at least one of the plurality of distance determining devices.

This application is a 35 U.S.C. §371 National Stage Application ofPCT/EP2010/060523, filed on Jul. 21, 2010, which claims the benefit ofpriority to Serial No. DE 10 2009 029 364.7, filed on Sep. 11, 2009 inGermany, the disclosures of which are incorporated herein by referencein their entirety.

BACKGROUND

The disclosure relates to a measuring device for measuring a distancebetween the measuring device and a target object with the aid of opticalmeasurement radiation.

Optical distance measuring devices are known which align a temporallymodulated light beam in the direction toward a target object whosedistance from the measuring device is intended to be determined. Thereturning light reflected or scattered from the target object aimed atis at least partly detected by the device and used for determining thedistance to be measured. In this case, a typical measurement range is ina range of distances from a few centimeters up to several 100 meters.

In order to be able to measure the distance from the target object usinga light beam, the light beam is temporally modulated in terms of itsintensity, for example. By way of example light pulses can be emittedand a propagation time of a light pulse from emission until detectioncan be measured and the distance from the target object can becalculated therefrom. For this purpose, however, very short light pulseshave to be emitted and very fast detection electronics have to be usedin order to able to obtain sufficiently accurate measurement results.Alternatively, a light beam can be temporally periodically modulated interms of its intensity and a phase shift between the emitted lightsignal and the detected light signal can be used to determine thepropagation time and thus the distance from the target object. Theprinciple of laser distance measurement is generally known by thedesignation “Time of Flight Ranging” for example with continuousmodulation of the intensity of the light beam.

Furthermore, so-called three-dimensional (3D) cameras are known inwhich, in addition to an optical imaging of an object to be captured,the respective distance between a region on the surface of the object tobe captured and the camera is also intended to be detected. For thispurpose, the camera has an imaging optical unit that projects an imageof the object sharply onto a surface of a detector arranged behind it.In this case, the detector has a multiplicity of pixels arranged in amatrix-like fashion. In this case, each of the pixels can determineimage information such as, for example, a color or light intensity ofthe light reflected from a surface region of the target object. Inaddition, information about a distance between the camera and thecorresponding surface region of the target object can be determined. Forthis purpose, the target object can be illuminated with temporallymodulated laser radiation and the radiation reflected back from thetarget object and imaged onto the detector with the aid of an imagingoptical unit can be used, by determining the time of flight, todetermine spatially resolved information about distances from therespective surface regions of the target object.

However, in addition to a spatially resolving detector having amultiplicity of pixels, such a three-dimensional camera also requires animaging optical unit in order to image each surface region of the targetobject precisely onto a pixel, wherein the detection signal determinedfrom said pixel can then be used for determining the distance from therespective surface region. This requires a comparatively complicatedfocusing optical unit and the possibility of individual evaluation ofdetection signals of each of the pixels.

In contrast thereto, simple distance measuring devices are used only fordetermining a distance between the measuring device and the targetobject or a point on the target object sighted by means of a laser beam.In this case, the distance does not need to be determined in a spatiallyresolved manner. It generally suffices to determine an averageddistance. Such distance measuring devices are often used in handhelddevices in order to determine within a room, for example, the distancefrom a specific location to surrounding target objects such as, forexample, walls or items of furniture. In this case, a handheld distancemeasuring device should preferably have a construction that is assimple, robust and cost-effective as possible, and should allow simpleoperation.

DE 10 2006 013 290 A1 discloses a device for optical distancemeasurement in which a detector of a receiving unit has a plurality oflight-sensitive areas which are separated from one another and which canbe activated separately from one another. In this case, each of thelight-sensitive areas has a photodiode, for example a PIN diode or anAPD (Avalanche Photo Diode), or a CCD chip as light-sensitive element.These light-sensitive elements determine an analog detection signalcorresponding to an intensity of the received light. The light-sensitiveareas can be selectively activated and combined in this way to form atotal detection area which can be matched as well as possible to apartial region of the detector area that is illuminated by a lightsource, in order in this way to improve a signal-to-noise ratio.

SUMMARY

There may be a need for a measuring device for optical distancemeasurement which, particularly in comparison with the conventionaldistance measuring devices described above, permits a simplifiedconstruction of electronic components used therein, in particular ofevaluation components for evaluating detection signals.

Furthermore, there may be a need for a distance measuring device whichhas as far as possible at least one of the following advantages:

-   -   expansion of an adjustment tolerance of a receiving optical unit        of the distance measuring device relative to a detector;    -   reduction of a complexity and requirements made of a receiving        optical unit;    -   increase in a dynamic range particularly in the measurement of        small distances;    -   optimization of a signal-to-noise ratio particularly in the        measurement of large distances; and/or    -   reduction of chip area of an integrated circuit that is required        for the evaluation.

The measuring device for optical distance measurement according to thedisclosure comprises a transmitting unit for emitting opticalmeasurement radiation toward a target object, a receiving unit having adetection area for detecting optical measurement radiation returningfrom the target object, and an evaluation unit having a plurality ofdistance determining units. In this case, the detection area of thereceiving unit has a multiplicity of pixels, wherein each pixel has atleast one light-sensitive element. Each of the multiplicity of pixels isconnected to the evaluation unit directly or indirectly via furtherinterposed components. The evaluation unit is designed in such a waythat detection signals of a plurality of pixels are forwarded to atleast one of the plurality of distance determining units, on the basisof which the respective distance determining unit determines distancedata which correlate with the distance between the measuring device andthe target object. The evaluation unit is designed to determine adistance between the measuring device and the target object on the basisof an evaluation of distance data that were determined by the pluralityof distance determining units.

The transmitting unit can be a light source, for example in the form ofan LED, a laser or a laser diode, which emits light in a temporallymodulated fashion toward the target object. In this case, the temporalmodulation can be effected continuously and/or periodically, for examplesinusoidally. It is also possible to emit pulse trains, for examplenon-periodically such as e.g. in the form of so-called pseudo noisepulse sequences.

In this case, each of the pixels can be connected to the evaluation unitdirectly or, for example, with the interposition of a multiplexerdesigned to selectively forward detection signals of a plurality ofpixels. What can be achieved in this way, for example, is that detectionsignals of individual pixels or of a group of pixels can be evaluated bythe evaluation unit independently of detection signals of other pixels.

The transmitting unit and the receiving unit are preferably designed andcoordinated with one another in such a way that optical measurementradiation returning from the target object under normal measurementconditions, that is to say, for example, in the case of measurementdistances of from a few centimeters up to a few 100 meters,simultaneously are illuminated a plurality of pixels. In this case,however, unlike in conventional 3D cameras, the fact that a plurality ofpixels are illuminated simultaneously is not intended to be used todetect an image of the target object or a spatial resolution with regardto the distance from individual partial regions on a surface of thetarget object, but rather is intended, as explained in even more detailfurther below, to make possible, inter alia, advantages with regard to adetection sensitivity and/or an adjustment tolerance. In this case, thedistance between the measuring device and the target object isdetermined on the basis of an evaluation of detection signals of aplurality of pixels, in particular of a plurality of the simultaneouslyilluminated pixels.

For this purpose, the transmitting unit can emit a measurement beamwhose cross section is large enough that that proportion of themeasurement beam which returns from the target object always illuminatesa plurality of pixels. In order to concentrate the measurement radiationreturning from the target object and to direct it onto the detectionarea, in order in this way to provide for a sufficiently strongdetection signal, a simple optical unit, for example in the form of oneor more lenses, can be provided within an optical path from thetransmitting unit to the receiving unit. Said simple optical unit can beconfigured in a cost-saving and complexity-reducing manner as anon-automatically focusing optical unit (“fixed focus”). Since such anon-automatically focusing optical unit having a fixed focal length canfocus a measurement beam returning from the target object onto thedetection area of the receiving unit optimally, i.e. with a smallestspot diameter, only when the target object is situated at the objectdistance from the measuring device which corresponds to the focal lengthand image plane, the number of pixels which are illuminatedsimultaneously by measurement radiation returning from the target objectcan vary in a manner dependent on a distance between the target objectand the measuring object. By way of example, the optimization of theoptical receiving system for receiving measurement radiation from targetobjects far away with a large object distance can mean that focal lengthand image distance should be chosen such that the geometrical imagingcondition is achieved for the large object distance. Consequently, at alarge distance, it is possible to achieve the smallest spot diameter inthe image plane (“the imaging is sharp”). By defining the focal lengthand image plane, it is possible for the number of pixels that areilluminated in the case of a target object situated closer to besignificantly greater than in the case of a target object far away. Inthe case of a target object situated closer, the returning measurementradiation can no longer be imaged sharply, with the result that theilluminated region of the detection area can become correspondinglylarger.

Since the detection signals of individual pixels can be evaluatedindependently of one another, the receiving unit and the evaluation unitcan be designed to determine a distance between the measuring device andthe target object on the basis of an evaluation of detection signalsexclusively from pixels onto which light from that area of the targetobject which is illuminated by the transmitting unit is radiated back.In other words, the evaluation unit can firstly determine in an initialmeasurement, for example, which of the pixels of the detection areaactually receive measurement radiation of the transmitting unit andwhich pixels merely detect background radiation, and can subsequentlyuse for the actual distance determination only the detection signals ofthe pixels illuminated by the measurement radiation. As a result, asignal-to-noise ratio can be considerably increased.

In order to be able to determine the distance between the measuringdevice and the target object, the evaluation unit can have a pluralityof distance determining unit (in some instances also known as “binningscheme”). A distance determining unit can be designed to determine datawhich correlate with the distance to be determined between the measuringdevice and the target object and from which therefore ultimately thedesired distance can be determined. By way of example, it is possible todetermine a time of flight of measurement radiation between an emissionfrom the transmitting unit until a detection of the measurementradiation returning from the target object on the detection area and todetermine the desired distance therefrom. For this purpose, the distancedetermining unit can compare information—provided by the transmittingunit—about the temporal modulation of emitted measurement radiation withdetection signals provided by the receiving unit. In the case of aperiodically modulated emitted measurement radiation, for example, acorresponding distance can be determined from the phase differencebetween an emission signal and a detection signal.

In principle, a single distance determining unit can suffice fordetermining a distance between the measuring device and the targetobject. In order to keep the number of distance determining units small,it can be advantageous to conduct the detection signals of individualpixels or of a group of pixels successively to a distance determiningunit for example with the aid of a multiplexer. On account of suchsequential processing of detection signals, a lengthening of a totalmeasurement duration can occur. Alternatively, each of the pixels can beassigned a dedicated distance determining unit. In this case, arespective distance can be determined from each of the detection signalsof the multiplicity of pixels, possibly temporally in parallel with oneanother, and, finally, from the multiplicity of distances determined, adistance between the device and the target object that is ultimately tobe determined can be determined for example by averaging. However, thiscan necessitate providing a very large number of distance determiningunits in the measuring device, which can make the construction and themanufacture of the measuring device complicated.

As it were as a middle way between these two extreme alternatives, aplurality of pixels can be connected to a distance determining unit andthe distance determining unit can therefore be designed to determine thedistance-correlated data on the basis of detection signals of theplurality of pixels. The evaluation unit proposed here therefore has aplurality of distance determining units and can be designed to determinethe distance between the measuring device and the target object on thebasis of the distance-correlated data determined by the distancedetermining units, for example by averaging.

By using a plurality of distance determining units, it is possible toreduce the time required for finding the pixels that receive measurementradiation, since variable combinations of pixels can be evaluated inparallel by means of skillfully chosen selection algorithms.

The number of light-sensitive elements or the area of the individuallight-sensitive elements contained in a pixel can be chosen in avariable fashion depending on the location of the pixel within thedetection area of the receiving unit. By way of example, it may be knownthat the measurement radiation returning from the target object canimpinge on the detection area of the receiving unit at a differentposition and/or with a different cross-sectional area depending on thedistance between the target object and the measuring device. The numberor the area of light-sensitive elements within a pixel can accordinglybe adapted in a location-dependent manner to the impinging lightintensity to be expected. By adapting the areas of the light-sensitiveelements and/or number of light-sensitive elements within a pixel, it ispossible to optimize a dynamic range of the measuring device. Byadapting the pixel areas to a laser spot size, it is possible tooptimize a signal-to-noise ratio.

If a non-automatically focusing optical unit designed to be imaging oroptimally focusing for target objects far away is arranged for examplein the light path between the transmitting unit and the receiving unit,for target objects far away the returning measuring radiation can befocused with a small spot diameter. Within such a region of thedetection area it can be advantageous for each of the pixels to containonly a single light-sensitive element or only a few light-sensitiveelements. If target objects situated closer are sighted by means of sucha fixed-focus measuring device, the returning measurement radiationcannot be focused on the detection area as a small spot, but ratherimpinges possibly in a defocused fashion on a larger partial area of thedetection area. Overall, in this case, more pixels are then illuminatedthan in the case of a target object situated far away. Therefore, it canbe advantageous, in edge regions of the illuminated partial region ofthe detection area, in each case to combine a plurality oflight-sensitive elements to form an individual pixel (or “sub-array” or“cluster”).

By way of example, the transmitting unit and the receiving unit can bearranged alongside one another along a parallax axis. Such so-calledbiaxial measuring systems can have the advantage that there is no needfor complex radiation splitting for selecting the returning measurementbeam. In this case, the measurement beam emitted by the transmittingunit and returning from the target object can impinge on the detectionarea at a different location along the parallax axis and have differentcross sections depending on the distance of the target object. In thiscase, it can be advantageous to vary the number of light-sensitiveelements contained in a pixel depending on the location of the pixelalong the parallax axis. In particular, it can be advantageous to choosethe number of light-sensitive elements contained in a pixel to besmaller in pixels near the transmitting unit than in pixels remote fromthe transmitting unit.

Alternatively, the transmitting unit and the receiving unit can bearranged coaxially with respect to one another. In the case of such amonoaxial measuring device, what can be achieved with the aid ofsemitransparent mirrors, for example, is that the center of that regionof the detection area which is illuminated by the returning radiationremains largely location-constant independently of the distance of thetarget object. However, the cross section of the illuminated region onthe detection area can still depend on the distance of the targetobject. A small illuminated spot can occur in the case of target objectsfar away and an optical unit having a long focal length, and a largerilluminated spot can occur in the case of target objects situatedcloser. It can be advantageous to choose the number of light-sensitiveelements contained in a pixel to be smaller in pixels near the center ofthe detection area than in pixels remote from the center of thedetection area.

Possible aspects, advantages and configurations of the disclosure havebeen described above with reference to individual embodiments of thedisclosure. The description, the associated figures and the claimscontain numerous features in combination. A person skilled in the artwill also consider these features, in particular also the features ofdifferent exemplary embodiments, individually and combine them to formexpedient further combinations.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the disclosure and partial aspects contained therein aredescribed below with reference to the accompanying figures. The figuresare merely schematic and not true to scale. Identical or similarreference symbols in the figures designate identical or similarelements.

FIG. 1 shows a measuring device for optical distance measurement inaccordance with one embodiment of the present disclosure.

FIG. 2 shows a schematic circuit of two light-sensitive elementsconnected to a combiner, for a measuring device in accordance with oneembodiment of the present disclosure.

FIG. 3 shows a plan view of a detection area of a receiving unit for ameasuring device in accordance with one embodiment of the presentdisclosure.

FIG. 4 shows a plan view of an alternative detection area of a receivingunit for a measuring device in accordance with one embodiment of thepresent disclosure.

FIG. 5 shows an individual light-sensitive element connected to adistance determining unit.

FIG. 6 shows two light-sensitive elements connected to a distancedetermining unit via a multiplexer.

FIG. 7 shows two pixels each having 9 light-sensitive elements, whichare connected to a distance determining unit via combiners andmultiplexers.

FIG. 8 shows a detection area of a receiving unit with pixels in whichthe number of light-sensitive elements contained in the pixels varies ina location-dependent manner and which are connected to a plurality ofdistance determining units via combiners and multiplexers.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a measuring device 10 for opticaldistance measurement according to the disclosure with the most importantcomponents for describing its function.

The measuring device 10 comprises a housing 11, in which a transmittingunit 12 for emitting optical measurement radiation 13 and a receivingunit 14 for detecting measurement radiation 16 returning from a targetobject 15 are arranged.

The transmitting unit 12 comprises a light source, which is realized bya semiconductor laser diode 18 in the exemplary embodiment illustrated.The laser diode 18 emits a laser beam 20 in the form of a light bundle22 visible to the human eye. For this purpose, the laser diode 18 isoperated by means of a control unit 24, which, by means of correspondingelectronics, generates a temporal modulation of an electrical inputsignal 19 of the laser diode 18. What can be achieved by such modulationof the diode current is that the optical measurement radiation 13utilized for distance measurement is likewise modulated temporally interms of its intensity in a desired manner.

The laser beam bundle 20 subsequently passes through a collimationoptical unit 26 in the form of an objective 28, which is illustrated inthe form of an individual lens in a simplified manner in FIG. 1. In thisexemplary embodiment, the objective 28 is optionally situated on anadjusting assembly 32, which, in principle, makes it possible to changethe position of the objective in all three spatial directions, forexample for alignment purposes. Alternatively, however, the collimationoptical unit 26 can also already be part of the laser diode 18 orfixedly connected thereto.

After passing through the objective 28, this results in a, for exampleamplitude-modulated, signal of the measurement radiation 13 in the formof an almost parallel light bundle 37, which propagates along an opticalaxis 38 of the transmitting unit 12.

In addition, a preferably switchable beam deflector 40 can also besituated in the transmitting unit 12, and allows the measurementradiation 13 to be deflected wholly or partly whilst bypassing thetarget object 15 directly, that is to say device-internally, onto thereceiving unit 14. In this way it is possible to generate adevice-internal reference path 42, which allows calibration oradjustment of the measuring device.

If a distance measurement is carried out by means of the measuringdevice 10, the measurement radiation 13 leaves the housing 11 of themeasuring device through an optical window 44 in the end wall 45 of themeasuring device 10. The opening of the optical window 44 can beprotected for example by a shutter 46. For the purpose of actualmeasurement, the measuring device 10 is then aligned toward a targetobject 15 whose distance 48 from the measuring device 10 is intended tobe determined. The signal 16 reflected or scattered at the desiredtarget object 15 forms returning optical measurement radiation 16 in theform of a returning beam bundle 49 or 50, a certain portion of whichpasses back into the measuring device 10 again.

Through an entrance window 47 at the end side 45 of the measuring device10, the returning measurement radiation 16 is coupled into the measuringdevice 10 and then impinges, as illustrated in FIG. 1, on a receivingoptical unit 52.

Two returning measurement beam bundles 49 and 50 for two differenttarget object distances 48 are depicted for illustration by way ofexample in FIG. 1. For large object distances, where large can beinterpreted as large relative to the focal length of the receivingoptical unit 52, the optical measurement radiation 16 returning from thetarget object 15 is incident approximately parallel to the optical axis51 of the receiving unit 14. This case is represented by the measurementbeam bundle 49 in the exemplary embodiment in FIG. 1. As the objectdistance becomes smaller, the returning measurement radiation 16incident in the measuring device is inclined more and more relative tothe optical axis 51 of the receiving unit 14 on account of a parallax.The beam bundle 50 is depicted in FIG. 1 as an example of such areturning measurement beam bundle in the near range of the measuringdevice.

The receiving optical unit 52, which is likewise merely symbolizedschematically by an individual lens in FIG. 1, focuses the beam bundleof the returning measurement radiation 16 onto the detection area 66 ofa receiving detector 54 provided in the receiving unit 14. The detector54 has a multiplicity of pixels for detecting the optical measurementradiation. Each of the pixels has at least one light-sensitive element.By means of the light-sensitive elements provided in the detection area66, which are arranged individually or in groups in combination inpixels in a matrix-like manner and are connected to an evaluation unit36, the incident returning measurement radiation 16 is converted into anelectrical signal 55 and fed for further evaluation in the evaluationunit 36.

The detection signals generated by an individual light-sensitive elementor a combination of light-sensitive elements can be fed to the distancedetermining units contained in an evaluation unit 36. A distancedetermining unit can sum the detection signals and generate therefrom asignal corresponding to a time-dependent intensity of the light signalimpinging on the respective light-sensitive elements or the lightintensity. By relating this signal to an excitation signal indicatingthe temporal profile of the photon rate emitted by the transmittingunit, it is possible to deduce a photon time of flight from thetransmitting unit toward the target object and back again to thereceiving unit. If the transmitting unit periodically modulates theemitted light sinusoidally, for example, it is possible to determine atime of flight from a phase difference between the emitted and detectedmeasurement radiation.

FIG. 2 shows two light-sensitive element 101, 101′, the detectionsignals of which are respectively forwarded to an OR gate 103. The ORgate 103 acts as a combiner 104 by taking up both detection signals fromthe first light-sensitive element 101 and detection signals from thesecond light-sensitive element 101′ and outputting a combined signal ofthese input signals at an output 105.

FIG. 3 schematically shows a detection area 110 of a detection unit 54for a laser distance measuring device with uncorrected parallax. Theillustration depicts circular laser spots 109, the diameter of whichvaries depending on a distances L between the measuring device and thetarget object, on the detection area 110. This assumes an ideal lenshaving a focal length f=30 mm, a diameter d=4 mm and a parallax of 5 mmfor the case of optimum alignment with regard to large distances. Thelaser radiation was assumed to have a divergence of 1 mrad in this case.In this configuration of the detection area 110 it is advantageous thatthe size of the pixels 111 or the number of the light-sensitive elements101 within respective pixels 111 increases along the parallax axis 113.In this case, the parallax axis is assumed to be the straight line ofintersection between a detection area plane and a plane spanned by theoptical axis of the receiving optical unit and the laser beam axis ofthe distance measuring device. It can be discerned that in a firstregion 114, in which the laser spot 109 impinges if the laser beam isradiated back from a target object far away, small pixels are providedwhich each contain only a single light-sensitive element. In a region115, in which the laser spot 109′ impinges if the target object is at adistance of approximately 0.5 to 1 m, larger pixels each having fourlight-sensitive elements are provided. In a further region 116, in whichthe laser spot 109″ impinges for the case of very close target objects,particularly large pixels having 8 or 16 light-sensitive elements areprovided. In this case, the receiving optical unit is optimized suchthat the best possible imaging quality, that is to say the smallestpossible laser spot diameter on the detection area, is achieved for thelargest distance of the target object.

In the case of large distances, the laser spot 109 is comparativelysmall on account of the sharp imaging. At the same time, theintensity—composed of returning measurement and background radiation—ofthe impinging light is comparatively low on account of the smallproportion of the measurement radiation from the target object far away.In the case of target objects positioned closer, overall moremeasurement radiation is reflected or scattered from the target objectback to the detection area 110. At the same time, the measurementradiation is no longer imaged sharply onto the detection area 110 by thefixed-focus receiving optical unit.

In total, for a geometrical consideration for a laser distance measuringdevice with a slightly divergent laser beam and a fixed-focus receivingoptical unit for the proportion of the received laser radiation, a lightintensity that decreases with the square of the distance arises in thedetector plane in the case of large distances and a light intensity thatis constant over the distance arises in the detector plane in the caseof small distances. By contrast, the intensity proportion of thebackground radiation is distance-independent to a first approximation.

With a location-dependent configuration—as illustrated in FIG. 3—of thesize of the pixels 101 contained in the detection area 110, what can beachieved, firstly, is that both in the case of large distances of thetarget object and in the case of small distances of the target object, alaser spot 109 in each case impinges on a plurality of pixels 111 andcan be evaluated by the latter. The size of the active detection areacan in this case be optimally adapted to the size of the laser spot andthe signal-to-noise ratio can thus be optimized. Secondly, with such alocation-dependent configuration, the dynamic range of thelight-sensitive elements can also be optimally utilized, since the lightintensity of the impinging light (laser proportion and backgroundproportion) is lower in the case of large distances than in the case ofsmall distances. In the case of the detector areas exposed to receivedmeasurement radiation only in the case of small distances, therefore,the area of the individual light-sensitive elements can be reduced. Inthe detector regions in which the intensity of the received measurementradiation remains almost constant, the number of light-sensitiveelements 101 contained in the individual pixels 111 can be increasedwith the area of the light-sensitive elements remaining the same.

FIG. 4 shows an embodiment of a detection area 110′ for a coaxial laserdistance measuring device or a laser distance measuring device withcorrected parallax. Such a correction can be achieved with the aid of anear-range element or alternative, known methods. In such a case, theimaging aberration as a result of the finite depth of focus of thereceiving optical unit substantially dominates, such that a concentricarrangement of the pixels having an identical size is advantageous. Alaser beam returning from a target object far away is focused well andgenerates a relatively small laser spot 109 in the vicinity of thecenter 122 of the detection area 110′, that is to say in the vicinity ofthe piercing point of the optical axis of the receiving optical unitthrough the detection area plane. A laser beam returning from a targetobject situated closer generates a laser spot 109″ having asignificantly larger diameter. In the vicinity of the center 122, thepixels 111 have a smaller area and a smaller number of light-sensitiveelements 101 contained therein than at a distance from the center 122 ofthe detection area 110′, that is to say at the edge of the detectionarea.

FIGS. 5 to 7 illustrate individual elements such as are used forrealizing a receiving unit in accordance with embodiments of the presentdisclosure, as a block diagram.

FIG. 5 shows a pixel 111 having an individual light-sensitive element101. The pixel is connected to a distance determining unit 130.

FIG. 6 shows two pixels 111, 111′ each having a light-sensitive element101, 101′. The pixels 111, 111′ are connected to a multiplexer 140,which forwards the detection signals supplied by the pixels 111, 111′selectively to a distance determining unit 130.

FIG. 7 illustrates an arrangement of two pixels 111, 111′ each havingnine light-sensitive elements 101, 101′. The detection signals from theindividual light-sensitive elements 101, 101′ are, if appropriate aftera temporal delay brought about by additional delay elements 150, 150′,respectively forwarded to a combiner 160, 160′. The delay can serve forthe compensation of propagation time differences and hence the temporalsynchronization of the light-sensitive elements of one pixel ordifferent pixels. The detection signals are combined with one another inthe combiners 160, 160′. The combined detection signals are conductedfrom the combiners 160, 160′ to a multiplexer 140 and from there on to adistance determining unit 130.

FIG. 8 shows a specific embodiment for a distance measuring device withcorrected parallax using such elements for N=92 pixels 111. In thiscase, 48 pixels have only an individual light-sensitive element, 24pixels each have four light-sensitive elements in a 2×2 arrangement, and20 pixels each have 9 light-sensitive elements in a 3×3 arrangement.Each pixel 111 having more than one light-sensitive element 101 isexactly connected to one combiner 160, 160′. Accordingly, there are 44combiners 160. The outputs of the pixels 111 having only onelight-sensitive element and of the combiners 160 are connected to inputsof K multiplexers 140. The outputs of the multiplexers 140 are in turnconnected to M≧2 distance determining units 130. In this case, itneither necessarily holds true that M=K nor that M=N. The connectionsfor three pixels 111 having different sizes and numbers oflight-sensitive elements are illustrated by way of example. An areaillustrated in a hatched fashion in FIG. 11 indicates an effectivedetector area 170 comprising those pixels 111 which are actuallyilluminated by the laser light of the laser spot 109 and on the basis ofwhich a distance measurement with respect to the target object can becarried out.

Finally, aspects and advantages of embodiments of the disclosure will besummarized again using different words:

One embodiment of the disclosure is based on the central concept ofadvantageously configuring the type of arrangement of individuallight-sensitive elements in pixels whose signals are combined beforethey are fed to a temporal evaluation unit (having a plurality ofdistance determining units) for further evaluation. The amount oflight-sensitive elements whose signals are combined by means of acombiner forms a pixel in this case.

The individual pixels can be operated independently of one another. Inparticular, it is possible to perform a phase evaluation of a continuouswave or alternatively a time-of-flight evaluation of a pulse for eachindividual pixel.

A combination of a plurality of light-sensitive elements to form pixelscan be spatially configured in such a way that the signal-to-noise ratiocan be optimized both in the case of large distances and in the case ofsmall distances in particular with strong background illumination with asmall number of distance determining units. This can be achieved bymeans of an adaptation—which is location-dependent over the detectionarea—of the size of the pixels or the number of light-sensitive elementswhich are combined to form a pixel.

The type of arrangement of optionally pixels having only onelight-sensitive element or pixels having different sizes and numbers oflight-sensitive elements, said type of arrangement being specificallyoptimized toward increasing the signal-to-noise ratio in a laserdistance measuring device, constitutes one of the distinguishingfeatures both with respect to conventional laser distance measuringdevices and with respect to 3D cameras. This arrangement can reduce therequirements made of alignment of an optical unit within the measuringdevice and can simultaneously contribute to an optimized signal-to-noiseratio, even if the receiving unit does not lie in the image plane of theoptical unit, as can occur in the case of fixed-focus systems, forexample.

A detection area can be given dimensions large enough that therequirements made of the alignment of the receiving optical unit can bereduced. Moreover, it is possible to minimize the influence of opticalimaging aberrations, in particular the aberrations as a result ofdefocusing on account of an excessively small depth of field. Therequirements made of the optical quality of the receiving optical unitcan be reduced as a result.

A further advantage can be the optimization of the signal-to-noise ratioparticularly in the case of large measurement distances with a highproportion of background light. This can be achieved by virtue of thefact that the effective detection area for all distances can beoptimally adapted to the size of the actually imaged laser measurementspot in the detection plane, that is to say can be minimized. Aftermeasurement has been concluded, the signals from exclusively thoseindividual light-sensitive elements or pixels having a plurality oflight-sensitive elements which actually receive laser radiation can beevaluated in a targeted manner. As a result, the effective detectionarea can be reduced and the noise contribution of the background lightcan be minimized, which can be tantamount to an improvement in thesignal-to-noise ratio.

A further advantage may consist in the fact that fewer distancedetermining units than light-sensitive elements are required on accountof the combination of a plurality of light-sensitive elements within apixel. This can reduce a required chip area of an integrated circuit.Particularly in the case of laser distance measuring devices whichgenerally operate with a fixed focal length, this advantage can play animportant part since the laser spot diameter can then vary in a mannerdependent on the distance of the target object. FIG. 6 illustrates thisfor a system in which the parallax error is not corrected. In order tooptimize the signal-to-noise ratio as described above by minimizing theeffective detection area, in the case of relatively large laser spotdiameters, that is to say generally in the case of relatively smalldistances of the target object, accordingly only a relatively lowresolution of the detector may be required as well. This circumstancecan be utilized by the location-dependent combination of light-sensitiveelements to form pixels.

Since the effective detection area, that is to say the area which istaken into account in the evaluation of the measurement, is generallysmaller than the total detection area, the number of required distancedetermining units can be reduced even further by also employingmultiplexing in addition to the combination of light-sensitive elements.With the aid of preliminary measurements, in this case the pixelsreceiving laser radiation can firstly be identified and subsequently bedistributed among the distance determining units for the actualmeasurement. If N is the total number of pixels having one or morelight-sensitive elements and M is the number of distance determiningunits available for evaluation, then it is necessary to carry out atmost rounded-up N/M preliminary measurements for identificationpurposes. The measurement task can therefore be carried out with a smallnumber of measurements, ideally with a single measurement.

A further advantage may reside in the fact that individual pixels can becalibrated independently of one another, for example with regard to aphase offset.

The invention claimed is:
 1. A measuring device for optical distancemeasurement, in particular a handheld measuring device, comprising: atransmitting unit for emitting optical measurement radiation toward atarget object; a receiving unit having a detection area for detectingoptical measurement radiation returning from the target object; and anevaluation unit having a plurality of distance determining units,wherein the detection area has a multiplicity of pixels, wherein eachpixel has at least one light-sensitive element, wherein the evaluationunit is designed in such a way that detection signals of a plurality ofpixels are forwarded to at least one of the plurality of distancedetermining units, on the basis of which the respective distancedetermining unit determines distance data which correlate with thedistance between the measuring device and the target object, and whereinthe evaluation unit is designed to determine a distance between themeasuring device and the target object on the basis of an evaluation ofdistance data that were determined by the plurality of distancedetermining units.
 2. The measuring device as claimed in claim 1,wherein the distance determining devices are in each case designed todetermine a time of flight of measurement radiation between emission bythe transmitting unit until detection of measurement radiation returningfrom the target object and to determine a distance therefrom.
 3. Themeasuring device as claimed in claim 1, further comprising: at least onemultiplexer in order to forward detection signals of individual pixelssequentially to a distance determining unit.
 4. The measuring device asclaimed in claim 2, wherein the evaluation unit is designed to determinethe distance between the measuring device and the target object on thebasis of the distances determined by the distance determining units. 5.The measuring device as claimed in claim 1, wherein at least some pixelseach contain a plurality of light-sensitive elements.
 6. The measuringdevice as claimed in claim 5, furthermore comprising: at least onecombiner designed to combine detection signals of light-sensitiveelements which are contained in an individual pixel.
 7. The measuringdevice as claimed in claim 5, furthermore comprising: at least one pulseshortener in order to temporally shorten a digital signal generated byan SPAD.
 8. The measuring device as claimed in claim 5, wherein thenumber of light-sensitive elements contained in a pixel varies dependingon the location of the pixel within the detection area of the receivingunit.
 9. The measuring device as claimed in claim 5, wherein an area oflight-sensitive elements contained in a pixel varies depending on thelocation of the pixel within the detection area of the receiving unit.10. The measuring device as claimed in claim 8, wherein: thetransmitting unit and the receiving unit are arranged alongside oneanother along a parallax axis, and the number of light-sensitiveelements contained in a pixel varies depending on the location along theparallax axis.
 11. The measuring device as claimed in claim 8, whereinthe number of light-sensitive elements contained in a pixel is smallerin pixels near the transmitting unit than in pixels remote from thetransmitting unit.
 12. The measuring device as claimed in claim 8,wherein the number of light-sensitive elements contained in a pixel issmaller in pixels near the center of the detection area than in pixelsremote from the center of the detection area.
 13. The measuring deviceas claimed in claim 1, wherein the transmitting unit and the receivingunit are designed in such a way that a number of pixels which areilluminated simultaneously by optical measurement radiation returningfrom the target object varies in a manner dependent on a distancebetween the target object and the measuring device.
 14. The measuringdevice as claimed in claim 1, furthermore comprising: anon-automatically focusing optical unit for directing opticalmeasurement radiation returning from the target object onto thedetection area.
 15. The measuring device as claimed in claim 1, whereinthe receiving unit and the evaluation unit are designed for the purposethat detection signals of individual pixels can be evaluatedindependently of detection signals of other pixels by the evaluationunit.
 16. The measuring device as claimed in claim 1, wherein thereceiving unit and the evaluation unit are designed to determine adistance between the measuring device and the target object on the basisof an evaluation of detection signals exclusively of pixels within aneffective detection area, onto which light from that area of the targetobject which is illuminated by the transmitting unit is radiated back.17. The measuring device as claimed in claim 1, furthermore comprising:at least one multiplexer designed to forward detection signals of aplurality of pixels selectively to the evaluation unit.